In general, phthalate compounds can be obtained by an esterification reaction of an acid, such as phthalic acid, terephthalic acid, isophthalic acid, or an anhydride thereof, with an alcohol. In order to neutralize catalysts used in the esterification reaction and remaining acid components after the esterification reaction, basic compounds such as sodium carbonate (Na2CO3), sodium hydroxide (NaOH), calcium carbonate (CaCO3) and potassium hydroxide (KOH) are used. Accordingly, impurities such as metal ions including Na+, K+, Ca2+ liberated from such basic compounds, metal salt compounds produced by binding with the metal ions, or other reaction by-products may remain in a trace amount in the phthalate compounds.
When a trace amount of these metal ions or metal salt compounds is contained in the phthalate compounds, there is no significant influence on the quality of the phthalate compounds themselves, but they can act as a catalyst poison to the hydrogenation catalyst used in the hydrogenation reaction of the phthalate compounds, thereby becoming one of the main causes for lowering activity of the catalyst. More specifically, the metal ions or metal salt compounds exist in a state of not being sufficiently dissolved or dispersed and can be readily adsorbed to the hydrogenation catalyst physically or chemically, and thus the activity of the catalyst is drastically lowered.
Further, during the hydrogenation reaction of the phthalate compounds (that is, a hydrogen addition reaction), the activity of the catalyst is continuously lowered. When the activity of the catalyst is lowered to a certain level, catalyst replacement is required. In this case, with frequent catalyst replacements, economic efficiency may be reduced due to a decrease in production along with an increase in the cost of operation and replacement.
Accordingly, there is a need for a method for regenerating a hydrogenation catalyst that acts as a catalyst poison after the hydrogenation reaction of a phthalate compound. In addition, there is a need for a method capable of solving the problem of cost increase and production decrease caused by catalyst replacement during the hydrogenation addition reaction.